Commonly known tension bushes are provided with a slot having face surfaces and edges opposite and in parallel to each other. The outer diameter of the bush is selected such that the slot is not closed upon insertion of the bush into a bore by pressing. The resilient tensional forces necessary to retain the bush in the bore depend on the reduction of the diameter of the bush upon insertion and determine the strength of the fit. The latter further depends on the thickness of the wall of the bush. Thus, an increased resilient tensional force may only be achieved by using thicker material. However, both the thickness of the wall and the extent of change in diameter can be varied in relatively narrow limits only since with a small diameter the thickness of the wall must not exceed a certain amount since either the material surrounding the bore will lose its stability or a bolt to be inserted into the bush must have a small diameter resulting in weakness of the joint coupling. Furthermore, sheet material having an excessive thickness cannot be processed by rolling.
German Patent Specification No. 1,157,856 discloses a fixing pin comprising a bush provided with longitudinal slot and used for securing units and parts of electrical devices together. To increase the tensional force one of the edges of the slot is provided with projections engaging the opposite edge at bridge portions spanning over openings provided close to the edge of the slot such that the bridges are deformed. This results in a type of interlocking of the slot edges. However, deforming the slots causes only a rather limited increase of the tensional force which might be sufficient for purposes of locking pins but insufficient for achieving an optimum fit for tension bushes used as bearings. Furthermore, the deformation of the bridges result in projecting of material into the interior of the bush which projections are unacceptable for bushes used as a bearing having narrow tolerances. In addition, there is a danger of damaging the surface of the bolt or shaft inserted into a bush.
Another type of a tension bush is disclosed in German Patent Application No. 2,918,350, having a slot formed by generally parallel edges the slot having a v-like form such that upon pressing-in of the bush into a bore an opposing pair of slot edges egage and deform each other. Though this results in an increase of the fixing forces very high pressing-in pressures are necessary in view of the engagement of the two opposing edges along the overall length of the bush. Such high pressure may cause undesireable changes in the form of the material surrounding the bore, in particular, with thin-wall housings. A typical example are chain sidebars having thin-wall bridges which might easily burst. A further drawback of the known tension bush consists in the fact that they may be used with bores only having very narrow tolerances since the diameter of the bush must be such that the sharp slot edges contact each other upon pressing-in of the bush and deform only slightly. On the other hand, if the diameter of the bore is too large it might happen that there is only an insufficient or no contact of the slot edges. Consequently, there is no increase in the fixing forces. With too narrow a bore the forces for pressing-in the bush rapidly increase with the danger of damage of the wall surrounding the bore or at least of deformation thereof.